In a wireless communication system, a transmitter station may utilize multiple (T) transmit antennas for data transmission to a receiver station equipped with multiple (R) receive antennas. The multiple transmit and receive antennas form a MIMO channel that may be used to increase throughput and/or improve reliability. For example, the transmitter station may transmit up to T data streams simultaneously from the T transmit antennas to improve throughput. Alternatively, the transmitter station may transmit a single data stream from all T transmit antennas to improve reception by the receiver station.
The MIMO channel may be decomposed into S spatial channels, where S≦min {T, R}. Each spatial channel may experience various deleterious channel conditions such as, e.g., fading, multipath, and interference effects. The S spatial channels may experience different channel conditions and may achieve different received signal qualities, which may be quantified by signal-to-noise-and-interference ratios (SNRs) or some other measure. The SNR of each spatial channel determines its transmission capacity, which is typically quantified by a particular data rate that may be reliably sent on the spatial channel. For a time variant MIMO channel, the channel conditions change over time and the SNR of each spatial channel also changes over time. The different SNRs for different spatial channels plus the time varying nature of the SNR of each spatial channel make it challenging to control a MIMO transmission.
There is therefore a need in the art for techniques to control a MIMO transmission.